[Cthulhu_]

I appreciate that he worked on it at least. Around the same era, someone else calculated the circumference of the earth (and that it was round) in a pretty accurate fashion (between −2.4% and +0.8% off) based on measuring shadows on equally sized posts at different locations on the same date. Googled, it was Eratosthenes, the cities were Alexandria and Syene/Assuan.

[ubutler]

One of my favourite episodes of Cosmos centres around Eratosthenes’ calculation of the circumference of the Earth: https://youtu.be/G8cbIWMv0rI?si=CuX49ki1GIvBLpeL

[drexlspivey]

How did they take measurements in two different cities at the same time without clocks?

[wmanley]

IIRC they walked directly north and measured at midday.